here is a guide that worked for me when had my 612 with TT
if the HG is unlocked then set it with ip address to 192.168.0.1
disable dhcp, (if not works then turn on dhcp again and set the range from 192.168.0.2 -100
obtain ip auto & dns servers, at the moment don't disable nat (it may have double nat issue but if you don't use port forward should be ok)
at the 2920
disable wan 1 because if both wan's are enable may stolen some cpu memory and gives you slower speeds
enable the wan 2 which is giga (wan > general set up)
WAN >> Internet Access> details page> set it at static or dynamic ip section
mode always on
mtu 1500 if is 1492 at the 612 but with this can practice later
Specify an IP address: 192.168.0.100
subnet i m not sure try 255.255.255.0 / 255
gateaway ip> 192.168.0.1
ok > reboot both devices
(also at the 2920 make sure its ip range is from 192.168.10 to over 100, lets say 150 or 200) Lan>General set up>Lan 1> details page
should be able to see the stats of the huwaei and also the pages of the 2920
by the way there is a new firmware out 3.6.7 so give it a fresh flash before start setting it ... using the *rst* file (resets everything to factory defaults) but it helps from previous firmware bugs conflicts issues
ftp://ftp.draytek.com/Vigor2920/Firmware/v3.6.7/